Boiler and water-wall tubing are susceptible to a number of forms of damage which can result in tube damage if left unchecked. Such tube failures remain the number one cause of forced outages and availability loss in fossil plants worldwide.
Corrosion-fatigue damage in water-walls has become a major issue for many utilities. The inability to adequately detect or size such damage has lead to many early failures that could have been avoided if proper inspection access was available. Internal inspection methods are commonly employed for heat exchangers and steam generator tubing.
Unlike other components associated with fossil power production, inspection of boiler and water-wall tubing is not routinely performed. Access to the inside surface of such tubing is complicated since inspection holes are typically not available. Accessibility to the inside surface of tubing would enable utilities to routinely inspect suspect areas within the tubing and should substantially reduce the number of forced outages associated with tube failures.
Commonly assigned U.S. Pat. No. 6,596,957 is directed to a method and apparatus and prefabricated replacement tube for localized water-wall repair, and is incorporated by reference as if fully written out below. Also, commonly assigned U.S. patent application entitled “Method For Repairing Heat Recovery Steam Generator Tube-To-Header” and filed on even date is incorporated by reference as if fully written out below.
Formerly, no recognized methods existed to access the inside wall of water-wall or boiler tubing to perform inspection for corrosion-fatigue damage of the inside diameter (ID) surfaces short of severing a section of the tube, inserting an inspection device, inserting a replacement tube section upon completion of the inspection, and manually welding the replacement tube in place. This approach was time consuming, costly, and could often result in inferior quality of replacement welds.